The DSL technology is a technology for data high-speed transmission via an Unshielded Twist Pair (UTP), which includes an Asymmetrical Digital Subscriber Line (ADSL), a Very-high-bit-rate Digital Subscriber Line (VDSL), an Integrated Services Digital Network Digital Subscriber Line (IDSL), a Single-pair High-bit-rate Digital Subscriber Line (SHDSL), and so on.
In various DSL technologies, in addition to the IDSL and SHDSL which transmit services via a baseband, other DSLs usually use a passband to transmit services, that is, frequency division multiplexing technology is adopted to transmit a DSL service and a Plain Old Telephone Service (POTS) on a single UTP. The DSL service is transmitted in the high frequency band, and a Discrete Multi-Tone Modulation (DMT) is adopted to modulate and demodulate the service signals, while the POTS is transmitted in a baseband section. The signals of the above two services are processed uniformly through a splitter/integrator.
In an access system where the DSL service and the POTS service coexist, the accessed DSL service may have multi-paths. At a central office and a user end, the multi-path DSL service signals and POTS service signals are processed through a DSL Access Multiplexer (DSLAM), as is shown in FIG. 1, which is a schematic structural view of an access system. The user end DSLAM 120 includes a user end transceiver unit 121 and a splitter/integrator 122. In an uplink direction, the user end transceiver unit 121 receives multi-path DSL information from a computer 110 and amplifies the received signals, and then sends the amplified multi-path DSL signals to the splitter/integrator 122. The splitter/integrator 122 integrates the multi-path DSL signals from the user end transceiver unit 121 and the POTS signals from a telephone terminal 130. The integrated signals are then transmitted through multi-path UTPs 140 and are received by a splitter/integrator 151 of the central office DSLAM 150. The splitter/integrator 151 splits the received signals, sends the POTS signals to a public switched telephone network (PSTN) 160, and sends the multi-path DSL signals to a central office transceiver unit 152. The central office transceiver unit 152 re-amplifies the received multi-path DSL signals, and sends the amplified signals to a network management system 170. In the downlink direction, the process of signal transmission is identical to that in the uplink direction, and will not be described herein again.
As different types of DSL services may be transmitted on each UTP, the different types of DSL signals may interfere with each other. In the prior art, the signals are modulated by using the DMT technology of frequency division multiplexing. Meeting the data rate of K−1 subscribers, the method maximizes the rate of the remaining subscriber, and satisfies a power constraint
                    ∑                  k          =          1                K            ⁢                          ⁢              S        k        n              ≤          P      n        ,in which Pk represents the maximum total power that can be sent by the subscriber k, and Snk,max represents the maximum total power that can be sent by the nth tone of the subscriber k.
In the research of the prior art, the inventor found that maximization of a line rate can meet the subscriber's requirement for the rate; however, with the emergence of a VOIP service and an IPTV service that have a high requirement for line quality, only meeting the requirement for the line rate may result in a decline in the line quality, such as voice delay and frame loss. Due to the unstable line running quality, the subscriber's experience is affected. Moreover, since the subscriber does not need a very high rate in most cases, the power in the system is wasted by adopting the method of maximizing the line rate, resulting in increase of crosstalk between the lines as well as the cost of the system.